Clean Sweep

February 19, 1986

MEXICO CITY — New engines for buses. Mandatory exhaust controls. Lower lead content for gasoline. And trees. Lots of trees -- 36 million of them, in fact. Those are some of the ideas urban planners unveiled Monday for Mexico City, one of the world's most congested and polluted cities. Already there are doubts about the plan's effectiveness. A police spokesman said his department knew nothing about the emission control checks police are supposed to start making next year. The ''100 group'' of influential artists and intellectuals said the environmental program does not go far enough.